1) Field of the Invention
The present invention relates to an oxygen absorbent composition absorbing water vapor which is used during preservation of metals, metallic parts, electrical and electronic parts, magnetic and optical parts, plastics, glasses, rubbers, adhesive tapes, photographic films, foods, medical drugs, unearthed metals and art objects in a hermetically sealed container in order to maintain the interior of the hermetically sealed container to a dried and oxygen-free state.
2) Prior Art
When metals or dry foods are preserved in a hermetically sealed container, the presence of oxygen and water vapor including moisture and water in a hermetically sealed container deteriorates their qualities during preservation. Hitherto, as methods for preserving these articles in a hermetically sealed container in a dried and oxygen-free state, the following methods have been known.
(a) A method comprising enclosing a drying agent and an article to be preserved in a container with a barrier property against both oxygen and water and replacing air in the container with nitrogen and then hermetically sealing the container.
(b) A method comprising enclosing both a drying agent and an oxygen absorbent together with an article to be preserved in a container having a barrier property against both oxygen and water vapor and then hermetically sealing the container.
However, the above-mentioned (a) method caused problems that the oxygen concentration in the hermetically sealed container was increased due to oxygen permeated the container and invaded into its interior, so that qualities of an article to be preserved were deteriorated.
On the other hand, the above-mentioned (b) method required much labor since it was necessary to enclose in a container two agents of commercial drying agent and commercial oxygen absorbent filled and enclosed into two separate small bags and to seal hermetically the container. Thus, it was desired to assemble the two agents into one agent with both drying function and oxygen absorbing function. For the purpose, it was considered to fill and enclose both a drying agent composition and an oxygen absorbent composition into one same small bag and to provide with both water vapor absorbing function and oxygen absorbing function in one small bag. However, substances absorbing oxygen such as iron and ascorbic acid possess common feature that water is indispensable in order to absorb oxygen. Therefore, when a mixture of a powdery oxygen absorbent composition and a powdery drying agent composition was enclosed in one small bag to make a product as a composition absorbing both oxygen and water vapor, there was a defect that the drying agent composition absorbed water in the oxygen absorbent composition, so that oxygen absorbent function itself was degraded.
Thus, an oxygen absorbent composition requiring no water for absorption of oxygen can be mixed with a drying agent composition. As an oxygen absorbent requiring no water, Japanese Patent Kokai (Laid-open) No. 56-155641 discloses an oxygen absorbent composition in which an unsaturated fatty acid compound(s) of an oxygen absorbent is (are) supported on a porous carrier. In order to provide such oxygen absorbent composition with an ability absorbing water vapor, separate drying agent composition may be mixed, However, in such case, there was a problem that total volume was increased by volume of the separate drying agent composition thus mixed, so that the size of a small bag to be hermetically sealed became large. The smaller total volume of the composition, the more advantageous is the cost in production.
An object of the present invention is to provide an oxygen absorbent composition absorbing water vapor and absorbing stably and rapidly oxygen in order to absorb and remove both oxygen and water vapor in a hermetically sealed container.
Japanese Patent Kokai (Laid-open) No. 56-155641 exemplifies zeolite, silica gel, alumina and activated carbon as porous carriers (hereinafter, xe2x80x9cporous carrier such as zeolitexe2x80x9d). The porous carriers such as zeolite are capable of functioning as drying agents and can be used as a carrier of an oxygen absorbent. However, when an unsaturated fatty acid compound(s) of oxygen absorbent was(are) supported on a porous carrier such as zeolite, there were problems that the oxygen absorbing velocity of the composition thus obtained was not only small, but also it depended on water content of a porous carrier such as zeolite and the higher the water content of a porous carrier such as zeolite, the more was required the time (induction period) necessary to start oxygen absorption, so that the oxygen absorbing performance became bad and unstable, e.g., in a low oxygen concentration of about 1%, an oxygen concentration of 0.1% or below could not be reached due to lowering of oxygen absorbing velocity. Further, there was also a problem that when a porous carrier such as zeolite was exposed to the atmosphere, moisture was absorbed in several hours to increase water content, so that it was difficult to preserve heat-dried a porous carrier such as zeolite of low water content in the state of low water content and to produce the composition.
The inventors have found that a composition mixed a liquid absorbing oxygen without requiring water with a specific solid drying agent absorbs water and absorbs also oxygen more rapidly than in case of supporting an oxygen absorbent on a porous carrier such as zeolite and have accomplished the present invention.
That is, the present invention provides an oxygen absorbent composition absorbing water vapor mixed a liquid (hereinafter, xe2x80x9cmixed liquid of (A) and (B)) mixed (A) an aliphatic compound(s) with an unsaturated group(s) and (B) a transition metal salt(s) with (C) at least one solid (hereinafter xe2x80x9csolid compound of (C)xe2x80x9d) selected from the group consisting of calcium oxide, calcium chloride and magnesium chloride.
As (A) an aliphatic compound(s) with an unsaturated group(s), aliphatic hydrocarbons with an unsaturated group(s), unsaturated fatty acids or fats and oils containing an unsaturated fatty acid(s) can be used. Further, as (B) a transition metal(s), at least one salt of metal selected from the group consisting of Co, Mn, Fe and Cu can be used.
As (A) an aliphatic compound(s) with an unsaturated group(s), (hereinafter, xe2x80x9c(A) aliphatic compound with unsaturated groupxe2x80x9d), aliphatic hydrocarbons with an unsaturated group(s), unsaturated fatty acids or fats and oils containing an unsaturated fatty acid(s) can be used.
Examples of the aliphatic hydrocarbons with an unsaturated group(s) include butadiene oligomers, isoprene oligomers, acetylene oligomers, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, chloroprene oligomers, unsaturated polyester resins and natural rubbers and a mixture or a copolymer of two species thereof or above. Among them, aliphatic hydrocarbons in which a viscosity of liquid is low are preferable since they are readily mixed.
Examples of the fatty acid compounds and the fats and oils containing an unsaturated fatty acid(s) include unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, arachidonic acid, parinaric acid, dimer acid and ricinoleic acid and fats and oils unsaturated fatty acid such as linseed oil containing esters of above-mentioned, soybean oil, tung oil, rice bran oil, sesame oil, cotton seed oil, rapeseed oil and tall oil, esters thereof and metal salts thereof. Further, as the unsaturated fatty acid, fatty acids obtainable from vegetable oils and animal oils, e.g., linseed oil fatty acid, soybean oil fatty acid, tung oil fatty acid, rice bran oil fatty acid, sesame oil fatty acid, cotton seed oil fatty acid, rapeseed oil fatty acid and tall oil fatty acid also can be used. Among them, unsaturated fatty acids in which a viscosity of liquid is low are preferable since they are readily mixed.
As (B) a transition metal salt(s) (hereinafter xe2x80x9c(B) transition metal saltxe2x80x9d), at least one substance selected from organic acid salts of Co, Mn, Fe and Cu can be used. Examples of (B) transition metal salt include metal salts of stearic acid, dimethyldithio carbamic acid, acetylacetonate, hexoate, oleic acid, linoleic acid, linolenic acid, naphthenic acid and tall oil fatty acid, which act as a catalyst to promote oxygen absorbing reaction of (A) aliphatic compound with unsaturated group. An organic acid salt(s) of metal such as Zn and Pb may be added to them as a promoter.
It is necessary that (A) aliphatic compound and (B) transition metal salt are preliminary mixed to form a liquid. The mixing is performed usually with heating at room temperature (25xc2x0 C.) or at a temperature of room temperature to about 80xc2x0 C. It is preferable to dissolve (B) transition metal salt in (A) aliphatic compound with unsaturated group since the oxygen absorbing performance of the composition is improved. The mixing proportion of (B) transition metal salt to (A) aliphatic compound with unsaturated group is 0.005 to 5 parts by weight and preferably 0.05 to 0.5 parts by weight of (B) transition metal salt per 100 parts by weight of (A) aliphatic compound with unsaturated group.
Further, the mixing proportion of solid compound of (C) to mixed liquid of (A) and (B) is 200 to 2000 parts by weight and preferably 500 to 1000 parts by weight of solid compound of (C) per 100 parts by weight of mixed liquid of (A) and (B),
When an oxygen absorbing substance to be used as an oxygen absorbent is a liquid, it is usually impregnated (supported) in a solid carrier in order to improve its oxygen absorbing velocity and to facilitate its handling. As conventional carriers to be used in an oxygen absorbent, in order to impregnate (support) a liquid of amount as large as possible in a carrier of a small volume and to make contact area with air wide, porous carriers, e.g., zeolite, activated carbon, paper, non-woven fabric, porous film, pearlite, activated clay sepiolite and clay minerals such as diatomaceous earth have been used.
Further, Japanese Patent Kokai (Laid-open) No. 56-155641 discloses an oxygen absorbent composition requiring no water for absorption of oxygen in which an unsaturated fatty acid compound(s) of oxygen absorbent is supported on a porous carrier such as zeolite.
The present invention is an oxygen absorbent composition mixed the mixed liquid of (A) and (B) and the solid compound of (C) without using above-mentioned conventional porous substances. The amount of the solid compound (C) able to form a mixture with the mixed liquid of (A) and (B) is smaller than an amount able to support the mixed liquid of (A) and (B) on a porous carrier since the solid compound of (C) is not a porous solid. Regarding the mixture of the mixed liquid of (A) and (B) with the solid compound of (C), it is observed that the solid compound of (C) is apparently coated with the mixed liquid of (A) and (B). However, the oxygen absorbing velocity per unit weight of the mixed liquid of (A) and (B) in case of mixing the mixed liquid of (A) and (B) with the solid compound of (C) is remarkably larger than that in case of supporting it on above-mentioned porous carrier or in case of supporting it on a drying agent such as magnesium oxide, potassium carbonate, soda lime and magnesium perchlorate absorbing water vapor by other chemical reaction.
As one of reasons for above-mentioned phenomenon, the following is considered. The oxygen absorbing reaction of (A) aliphatic compound with unsaturated group is hindered in a high humidity such as 100% RH since (A) aliphatic compound with unsaturated group is a hydrophobic substance. Water is generated with progression of a chemical reaction of (A) aliphatic compound with unsaturated group and oxygen. It is considered that generated water hinders the oxygen absorbing reaction. In the present invention, (A) aliphatic compound with unsaturated group contacts the solid compound of (C) as a carrier in a solid-liquid phase. Therefore, it is considered that generated water is properly removed by a chemical reaction with the solid compound of (C) to depress lowering of the oxygen absorbing velocity, so that the oxygen absorbing velocity becomes larger than that in case of supporting it on above-mentioned porous carrier.
The composition of the present invention is enclosed in a gas-permeable packing material formed of a base sheet such as paper, non-woven fabric and plastic and then hermetically sealed in a container with a barrier property against oxygen and water vapor together with an object to be preserved to use. The composition can be used property in a form of powder, granule, tablet and sheet.
The present invention will be described in more detail below, referring to Examples, which are not intended to limit the scope of the present invention.